There are several industrial and commercial buildings which now exceed 60 stories or more. These buildings all need tall cranes to help transport the supplies to the upper floors. There are cranes that are operated from the rear of trucks or other types which have their own vehicle attached. Tower cranes are the largest types offered on the market.
Tower cranes are the stand-alone structures which are often seen on high-rise building projects. Usually, they are part of a major city's downtown skyline. Wherever new construction like for instance skyscrapers or apartment buildings and commercial facilities like for instance shopping center are being built, chances are a crane would be on site.
Types
The two major kinds of cranes can be differentiated by the way in which their jib or boom raises materials. The jib is the metal frame that extends from the main section. On a flat tower crane, the jib remains horizontal when it lifts items. On a luffing kind of tower crane, the jib could ratchet to upward or downward angles. The lifting capacity for both kinds could range from 30 pounds to 10,000 pounds
Body
The body of the crane is composed of a mast. This is a vertical steel frame that is a combination of individual sections. In order to increase the overall height of the machine, sections are added. The mast extends upward to where the desired height is, to the control module, which is a small room which has glass windows on all four sides or to the tower as it is also called. The driver of the crane works from inside of the tower.
Lift
The crane utilizes a braided metal cord to lift supplies. This cord extends out from a motor located next to the control module to the end of the boom or jib. There is a pulley system located at the end of the jib, through which the cord is positioned and lowered down. The jib which holds the cord becomes balanced by a counter jib located on the tower's opposite side. The counter jib has weights. These weights help to prevent the crane from toppling over when heavy materials are carried.